The need frequently arises in a wide variety of mechanical contexts to releasably secure together cylindrical members, e.g., tubes or rods. In some cases it is desirable to attach first and second cylindrical members in coaxial relation. Devices for achieving such coaxial attachment of cylindrical members are disclosed in U.S. Pat. Nos. 3,419,227, 4,124,258, 4,365,535, and 4,585,367. All of these devices include eccentric ring cams which are designed and rotatably mounted so as to secure the outer cylindrical member to the inner cylindrical member with a force that varies as a function of the rotational position of the ring cam.
In other cases it is desirable to attach elongate cylindrical members in end-to-end relation. U.S. Pat. Nos. 4,076,437 and 4,261,559 disclose devices for achieving such end-to-end attachment of cylindrical members. The devices disclosed in these patents include eccentric ring cams for securing one of the members to the other with a force that varies as a function of the rotational position of the ring cam.
A third class of devices exists for releasably securing a first tubular member to a second tubular member so that the axis of the first member extends transversely to the axis of the second member. Such devices are used, for instance, in the manufacture of tubular backpack frames for securing the ends of horizontally-extending members to the ends or midlength portions of vertically-extending members. One such device is used in backpack frames of the type manufactured by JanSport Corporation of Everett, Wash. This device consists of a housing having a first bore for receiving one end of a tubular member and a second bore, extending perpendicular to the first bore, for receiving a midlength or end portion of a second tubular member. One end of the first tubular member is axially and rotationally secured to the housing within the first bore using a bolt which extends through the housing so as to intersect the first bore and the first member positioned therein. The second tubular member is secured within the second bore via a set screw which engages the outer surface of the second member. The second member may be moved axially and rotationally relative to the first member by loosening the set screw and then moving the second member relative to the first member as desired. Once the desired rotational and axial position is achieved, the second member is secured relative to the first member by tightening the set screw.
Although the above-described backpack frame tube coupler device does permit a first tubular member to be releasably secured in selected axial and rotational relation to a second tubular member, the device suffers from several drawbacks which limit its utility. First, the set screw of the device can only be locked and unlocked with a screwdriver or other suitable tool. Because adjustment of a backpack frame is occasionally required during use of the backpack, a screwdriver or other appropriate implement must be carried on backpacking trips. Certain backpack users find the need to carry such tools objectionable. Second, if the set screw in the device is tightened sufficiently to engage the outer surface of the second tubular member but not tight enough to lock the second tubular member within the housing, the possibility exists, over time, that the set screw will score a portion of the outer surface of the second member. Such scoring may result in premature failure of the second tubular member.
Thus, a strong need exists for a locking device for releasably securing together first and second elongate cylindrical members in transversely extending relation which permits the first member to be moved axially and rotationally relative to the second member when in the unlocked position, and which secures together the first and second members when in the locked position, which device is operable between the locked and unlocked positions without resort to a screwdriver or other tool.